Preparation of methacrylic acid and esters



Patented Mar. 15,1938

PATENT- OFFICE PREPARATION OF METHACBYLIC ACID AND ESTERS Donald J.Loder, Wilmington, Del., assignor to E. I. du Pont de Nemours & Company,Wilmington, Del., a corporation of Delaware No Drawing. Originalapplication February 16,

1932, Serial No. 593,411. Divided and this application January 12, 1933,Serial No. 651,367

3 Claims.

This invention relates to a process for the preparation of esters of theunsaturated monocarboxylic aliphatic organic acids and more particularlyto the preparation of acrylic and methacrylic (alphamethyl acrylic)acid'esters from propionic and isobutyric acids. This application is adivision of my copending, application Ser. No. 593,411, filed February16, 1932.

According to the present invention the esters of the unsaturated acidsmay be obtained, in the following manner. The saturated monocarboxylicacid is first-halogenated, in order to substitute for one or more of itshydrogen atoms, a halogen atom. The thus halogenated acid is thenesterified, by means of an alcohol, to give an ester of the saturatedhalogenated acid. Subsequent to esterification, the halogenated ester isdehydrohalogenated (hydrogen halide is split oif) whereupon anunsaturated linkage is formed within the molecule and an ester, of anunsaturated monocarboxylic aliphatic organic acid, is obtained. While Iprefer, generally, to prepare the ester in the above manner, analternate method, in some instances, maybe employed. Subsequent tohalogenation, the compound is dehydrohalogenated and then esterified.This alternate procedure is not usually as applicable as the former,with equally advantageous results, due to the fact that a number of theunsaturated acids are not as stable per se as the ester of those acids.Accordingly, by arranging the steps of the process in my preferredmanner the unsaturated acid is never present as such and when theunsaturated linkage is produced, it is produced in the ester.

I will now describe several examples illustrating my process but it willbe understood that I will not be limited by the details thereof.

Example 1.Isobutyric acid containing 10% by weight of sulfur was heatedfor 6 hoursat approximately 130 C. while an excess of chlorine gas waspassed into the liquor. A product containing the following ,compoundswas obtained:

' Percent Alpha chlorisobutyryl chloride 17.9 Alpha chlorisobutyric acid40.7 Alpha chlorisobutyric anhydride 13.9 Beta chlorisobutyric acid 19.6Unconverted and lost 6.9

One hundred parts by volume of the above product was then refluxed atatmospheric pressure, in the presence of one part sulfuric acid, with160 parts of methanol. Esterificationwas substantially completed at theend of two hours and the esteriiled and chlorinated acid was thendistilled from the side products of the esteriiication. The thusesteriiied and chlorinated isobutyric acid was then vaporized and passedat atmospheric pressure and a temperature of 300C. over a silica gelcatalyst. 25% of the chlorinated ester was converted to the unsaturatedester. This ester, the methyl ester of methacrylic acid, has a boilingpoint of 100 C.

Example 2.-A rapid stream of chlorine gas was passed thru propionic acidcontained in a pyrex flask, which was radiated with a 100 watt lampduring 3 hours; the following chlorinated compounds were obtained:

Percent Alpha chlorpropionic acid 34-0 Beta chlorpropionic acid 39-6Alpha beta chlorpropionic acid 26.4

chlorpropionic acid was then dehydrochlorinated,one part ofbeta-chlorpropionic acid and two parts of water being vaporized and, ata temperature of 300 C. and a pressure of one atmosphere, passed over asilica gel catalyst. The acrylic 'acid was extracted, from the condensedproducts of the dehydrochlorination process, with ether, the etherdried, and removed from the acid by distillation. One hundred parts ofthe acrylic acid were then refluxed with 130 parts of methanol in thepresence of 1% sulfuric acid and the methyl ester of acrylic acidformed, after refluxing for one hour, was separated by distillation.

It has a boiling point of 80 C.

Anymodification of my invention will come within the scope thereofwithout sacrificing any .of the advantages that may bederived therefrom.

I claim:

1. Process for the preparation of an ester of methacrylic acid whichcomprises halogenatlng isobutyric acid, to a monohalogenated acid,catalytically dehydrohalogenating the halogenated. acid to formmethacrylic acid and esterifying the methacrylic acid.

2. A. process for the production of methyl methacrylate which compriseshalogenating isobutyric acid in the alpha position in the presence of ahalogenation catalyst, catalytically dehydrohalogenating thehalogenated. acid in the presence of a dehydrohalogenating catalyst toform methacrylic acid, and esterifying the methacrylic acid withmethanol to methyl methacrylate in the presence of an esterifyingcatalyst.

3. A process for the production of methyl methacrylate which compriseschlorinating isobutyric acid in the alpha position in the presence of asulfur catalyst, catalytically dehydrochlorinating thealpha-chlorisobutyflc acid in the presence 01' a silica gel catalyst toform methacrylic acid, and esterifying the methacrylic acid withmethanol to methyl methacrylate in the presence of sulfuric acid.

DONALD J. LODER.

